264 NEAV UNIONID^, MELANIDiE, ETC., 



tant marks of growth ; umbonial slope rounded and inflated ; posterior slope rather 

 wide, elliptical, with an indistinct furrow on each valve ; cardinal teeth large and 

 very much divided in each valve; lateral teeth very long, lamellar, curved and 

 beautifully granulate; anterior cicatrices confluent, very large and very deeply 

 impressed; posterior cicatrices confluent and well impressed ; dorsal cicatrices placed 

 across the centre of the cavity of the beaks; cavity of the shell rather deep and very 

 wide ; cavity of the beaks shallow and rounded ; nacre beautifully silver-white and 

 iridescent. 



Remarl's. — It is much to be regretted that a single specimen only of this fine 

 species, and without the soft parts, should have been procured. In some respects it 

 resembles some of our North American species, but that unerring characteristic of 

 divergent folds of the tips emphatically places it as an inhabitant of the fresh waters 

 of South America. In outline it approaches Weldonensis (nobis) and Charhttensi& 

 (nobis), as well as some varieties oi complanatus (Solander), but it is not so wide. In 

 the cardinal teeth it differs entirely from these. In outline it also approaches 

 Uruguayensis (nobis), but it differs much from that species in outline as well in the 

 cardinal and lateral teeth. The regular ellipse, the smooth polished umbos and the 

 much divided large cardinal teeth well characterize this species. In each valve the 

 cardinal tooth is divided into six compressed corrugate parts, larger or smaller, and. 

 the lamellar teeth are beautifully granular and iridized. Although the substance of 

 the shell is very thick, and the anterior cicatrices deeply impressed, the two lower 

 ones are confluent, while the third, — the upper one not usually noted,— is deeply 

 impressed and distinct from the great one beneath. In the lateral tooth of the left 

 valve the upper division is exceedingly small in this specimen, and it may be a 

 general character of the species. 



Unio locellus, pi. 33, fig. 79. 



Testa iKvi, elliptica, valde inflata, inasquilaterali, postice subrotundata, autice subtruncata ; valvulis 

 tenuibus ; natibus subprominentibus, tumidis, ad apices divaricate undulatis ; epidermide tene- 

 broso-fusca, obsolete radiata, antice striata; dentibus cardinalibus parvis, valde compressis, valde^ 

 obliquis, in utroque valvule duplicibus ; laf.eralibus parviusculis, lamellatis ; margarita cajruleo- 

 alba et iridescente. 



Shell smooth, elliptical, very much inflated, inequilateral, somewhat rounded be- 

 hind, subtruncate before ; valves thin ; beaks rather prominent, swollen, with diverg- 

 ent folds at the tips ; epidermis dark brown, obscurely rayed, striate before ; cardinal, 

 teeth small, very much compressed, very oblique and double in both valves ; lateral 

 teeth rather small and lamellar; nacre bluish white and iridescent. 

 Proc. Acad. Nat. Sci. 1866, p. .34. 



